CcoS from Rhodobacter capsulatus has been shown essential for incorporation of redox-active prosthetic groups (heme, Cu) into cytochrome cbb(3) oxidase. FixS of Bradyrhizobium japonicum appears to have the same function. Members of this family are found so far in organisms with a cbb3-type cytochrome oxidase, including Neisseria meningitidis, Helicobacter pylori, Campylobacter jejuni, Caulobacter crescentus, Bradyrhizobium japonicum, and Rhodobacter capsulatus.